The present invention generally relates to the field of explosive detonation and inertial confinement research, and more specifically to the use of flyer plates to detonate explosives and drive fusion reactions. The invention is a result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
Flyer plates have been used for detonating explosives since their invention in the late 1960's. Originally, these flyer plates were electrically operated, utilizing an electrically produced plasma to accelerate the plate. It was subsequently discovered, after development of the laser, that laser induced plasmas could be used for plate acceleration.
Current laser initiated explosives or energetic materials operate by either of two methods: thermal runaway, or exploding a metal film to generate a high temperature in a manner similar to an exploding bridgewire. The first of these, thermal runaway, is a slow process requiring a period ranging from several hundred microseconds to several milliseconds to attain plate acceleration. Additionally, thermal runaway requires the addition of undesirable additives to the energetic material in order to reduce energy and thermal requirements to a practical level. The second, the exploding metal film, is effective for low density (.apprxeq.0.5 Theoretical Maximum Density-TMD) secondary explosives, but is not effective to produce detonation at reasonable energies for high density (.apprxeq.0.9 TMD) explosives.
There is currently significant interest in inertial confinement fusion, where large amounts of energy are directed at a sphere of fuel. Although laser beams are now being used in testing, it is conceivable that multiple flyer plates could be shot at the fuel sphere, or that an imploding flyer plate could be on the fuel sphere. The flyer plate may reduce or eliminate the pre-heat problem with large high power lasers. The invention also finds application in one-dimensional impact of metals or other materials used in shock physics and high strain rate materials research.
The basic prior process for accelerating foils by laser beams involves focusing a laser beam on a free-standing foil in order to convert a portion of the thickness of the foil into a plasma. This plasma will drive a segment of the foil toward a target. Conventional laser interaction with metals produces penetration of the laser beam into the metal of only a few hundred angstroms. The energy deposited in the metal by the laser results in formation of a plasma within a few nanoseconds This metal plasma expands and continues to absorb the incoming laser energy, and may continue to convert more of the metal foil to plasma. The plasma expansion decouples the remaining laser pulse energy from the metal surface, resulting in low efficiency energy transfer from the laser to the metal foil. Because of this, the thickness of the foil remaining in the solid phase is uncertain and uncontrolled. Too great a conversion of the metal foil to a plasma may result in insufficient kinetic energy being delivered to the target.
The present invention solves these problems, and can control the thickness of the foil fired toward the target. The invention can also provide higher velocity flyer plates, thereby transferring a higher level of kinetic energy to the target.
It is therefore an object of the present invention is to provide laser launched flyer plates of a determinable mass.
It is another object of the present invention to provide flyer plates which will transfer a high amount of kinetic energy to a target.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.